A guidance system for a recently developed missile system employs a glass fiber optic to transmit the signal from the launch site to the missile in flight. A missile systems which employs such a signal transmission system is the Fog-M (i.e., fiber optic guided missile). The fiber optic or glass fiber is connected at one end to the missile guidance system and to the signal source at the other end. The fiber optic is wound on a bobbin from which the fiber optic payout takes place during missile flight. The signal is transmitted through the wound fiber optic material on the bobbin to link the missile during flight with the signal source.
The glass fiber is produced from a high purity silica preform rod wherein the preform rod is heated to its yield point at about 2000.degree. C., and a fiber is drawn from the heated preform. The manufacturing process must be controlled to produce fibers of uniform diameter and mechanical strength. For example, a mechanical strength of optical fibers in excess of 2.times.10.sup.5 psi is a desirable feature for certain specialized application (e.g., optical waveguides employing lengths of fiber).
Both mechanical strength of the fiber when manufactured and the ability of the fiber to retain its strength when stored are equally important. During storage the loss of mechanical property values can take place in addition to the loss during fiber drawing. Lack of mechanical strength is due to submicron flaws in the surface attributed, mainly, to chemical attack by atmospheric contaminants (e.g., moisture) during and after fiber drawing. Attempts to solve these problems have been studied by applying organic coating to the fiber following the drawing of the fiber. Failure resulted because those organic coatings are not impervious to moisture or hydroxy penetration. The penetration by moisture or hydroxy resulted in reduced strength of the coated fiber during periods of storage and/or use.
U.S. Pat. No. 4,227,907 issued to James A. Merritt and assigned to the United States of America as represented by the Secretary of the Army, Washington, D.C. disclosed a laser photochemical synthesis coating on optical fiber. As described hereinabove, the fiber which is drawn from a heated preform is immediately hermetically sealed with a layer of silicon nitride of about 0.02 to about 0.20 micrometer thickness. The Si.sub.3 N.sub.4 is deposited by laser photochemical reactions which forms the Si.sub.3 N.sub.4 on the freshly drawn silicon optical fibers in an atmospheric controlled chamber in a continuous operation which employs the reactant gases, SiH.sub.4 and NX.sub.3, wherein X is selected from hydrogen and/or fluorine.
The drawn fiber optic material when received from the manufacturer is coated with a buffer coat which can be an organic compound (e.g., methyl methacrylate, epoxy acrylates (Desota 95 008), polyimides, polyquinolines, and polsilazanes), or an inorganic compound such as Si.sub.3 N.sub.4. The drawn fiber optic material has a diameter from about 80 to 125 microns or from about 80 to 125 micrometers. The buffer coat when of organic origin adds to this diameter to a total diameter of fiber optic material plus buffer coat to equal about 250 microns. The inorganic coated fiber optical material when coated by the laser photochemical synthesis method increases the diameter by a smaller amount since the coating of Si.sub.3 N.sub.4 ranges from about 0.02 micrometers to about 0.20 micrometers.
An additional requirement for glass fiber coated with a buffer coat prior to being wound on a bobbin is to ensure that the fiber optic materials payout evenly from the bobbin to avoid breakage or malfunction of the fiber optic connection between the missile and the signal source sending the signal.
Advantageous would be material for which easy application in the form of a coating is achieved and which provides enough adhesive qualities to the fiber optic material having the buffer coating to thereby hold the fiber optic material in place on the bobbin during storage under wide variations temperatures and vibration conditions. Of particular advantage and a requirement for proper functioning is to provide a material which imparts adequate adhesive properties to allow consistent and uniform payout of optical fiber over wide temperature ranges and after storage at a wide range in temperature (-65.degree. F. to +165.degree.).